well that is the question of the day if the 4.2 battery will fit the 4.0 anyone out there with both? aside from that there are some cheap ones available, check in the accessories sticky I posted a link to the spare I bought from amazon. As for battery life there are many things you can do, scroll down to the post where I quoted someone else and do all those tricks http://anythingbutipod.com/forum/showthread.php?t=68257 with that I can leave my 4.0 on all night (midnight to 2 PM) and only drop 1 or 2 percent, if those aren't enough for you there is a guy developing a new ROM for are players here http://forum.xda-developers.com/show...0#post27454990 that seems to make it even better.

I thought this would be a good thread to post this information on as I have researched the SGP 4.0 battery:

SGP 4.0 Battery Model Number: EB494353VA
Capacity Size: 1200Mah

Notes:

- The battery is the same or is a compatible fit to the batteries used in the Samsung Dart T499 & DoubleTime i857 phones.

- I have seen a compatible battery number with smaller capacity. (800 or 1000). I have seen listings for batteries claiming to have a higher capacity but my guess is they're either bogus or thicker then the battery that comes with the SGP 4.0.

I have a SGP 4.0 and an SGP 4.2. They use different batteries. The 4.2 battery is quite a bit larger and won't fit the 4.0.

I've bought spare batteries for both. The part numbers are EB484659VU for the 4.2 and EB494353VA for the 4.0

For those of you with a 4.2 that want spare batteries, here's a link to the most recent one I bought:http://www.amazon.com/gp/product/B00...ls_o01_s00_i00
That's made by Anker and it's a good battery. As good as the one that came with the 4.2. I bought a couple of Samsung batteries from Amazon and one was completely defective and warped so it wouldn't even fit in the player and the other was okay but it arrived completely dead. It only charges to about 90% to 95% and doesn't last long. I think they've been on the shelf too long. They're batteries that Samsung use in some of their older phone models, I guess.

For what it's worth the 4.2 lasts about 30% longer on a charge. Until I got it I thought the 4.0 was the perfect device to keep in my shirt pocket but the 4.2 replaced it happily and I ain't going back. This thing is great.